Food Allergy in Dogs

One of the most common conditions affecting dogs is allergy.  In the allergic state, the dog's immune system "overreacts" to foreign substances (allergens or antigens) to which it is exposed.  These overreactions are manifested in three ways.  The most common is itching of the skin, either localized (one area) or generalized (all over the dog).  Another manifestation involves the respiratory system and may result in coughing, sneezing, and/or wheezing.  Sometimes, there may be an associated nasal or ocular (eye) discharge.  The third manifestation involves the digestive system, resulting in vomiting or diarrhea.

Types of Allergy

There are five known types of allergies in the dog: contact, flea, food, bacterial, and inhalant.  Each of these has some common expressions in dogs, and each has some unique features.

Food Allergy

A food allergy is a condition in which the body’s immune system reacts adversely to a food or an ingredient in a food.

Any food or food ingredient can cause an allergy.  However, protein, usually from the meat source of the food, is the most likely offender.  Proteins commonly found in dog foods are derived from beef, chicken, lamb, and horsemeat.

Lamb and Rice Diets

Although many people think lamb and rice diets are hypoallergenic, they are not.  They are not inherently less likely to cause allergy than other diets.  However, they have this reputation.  Here is why.

Several years ago there were no dog foods on the commercial market that contained lamb.  A manufacturer of prescription dog foods formulated a food from lamb that was suitable for allergy testing, which will be explained below.  Because of that situation, lamb-based dog food was considered “hypoallergenic.” 

Food Allergy Testing

Dogs are not likely to be born with food allergies.  More commonly, they develop allergies to food products they have eaten for a long time.  The allergy most frequently develops in response to the protein component of the food; for example, beef, pork, chicken, or turkey.  Food allergy may produce any of the clinical signs previously discussed, including itching, digestive disorders, and respiratory distress.  We recommend testing for food allergy when the clinical signs have been present for several months, when the dog has a poor response to steroids, or when a very young dog itches without other apparent causes of allergy.  Testing is done with a special hypoallergenic diet.  Because it takes at least 4 weeks for all other food products to get out of the system, the dog must eat the special diet exclusively for 4-8 weeks (or more).  If positive response occurs, you will be instructed on how to proceed.  If the diet is not fed exclusively, it will not be a meaningful test.  We cannot overemphasize this.  If any type of table food, treats or vitamins are given, they must be discontinued during the testing period.  There may be problems with certain types of chewable heartworm preventative, as well.  Your veterinarian will discuss this with you.

Because dogs that are being tested for inhalant allergy generally itch year round, a food allergy dietary test can be performed while the inhalant test and antigen preparation are occurring.